The diazo type process requires a transluscent original and involves the exposure of a sensitized emulsion coated upon either one or both sides of an acetate or polyester film; diazo materials also include emulsions on paper and cloth. Emulsions on both sides of the film permits the development of more intense images and increases the quality of the projected light.
The development of diazo type materials is generally a function of time, temperature, and, with most materials, the ambient humidity. Most systems employ anhydrous ammonia, in steel cylinders, as the developing agent. A separate container storing water provides the humidity. Such systems must of necessity be semi- or fully automatic with considerable controls, both valve and timing, to ensure proper flow of ammonia at constant pressure as the tank pressure reduces with use. The conventional exposure of diazo type materials is likewise complicated and requires extremely close and uniform spacing between the original and the sensitized film because of the high resolution requirements of the reduced size images. Thus far, commercial arrangements tend to be extremely complex and cumbersome.